Generally, as understood by the present inventors, state of the art audio ICs for audio playback can have several limitations that can create engineering and user trade-offs between power dissipation and signal to noise ratio (SNR) as well as dynamic range (DR). In one instance, a best in class portable audio CODEC (i.e. capable of encoding or decoding a digital data stream or signal) has reported a MPEG-1 or MPEG-2 Audio Layer III (MP3) quiescent power at 4 milliwatts, and a best SNR is 101 dB (Amplitude.) However, these parameters are not achieved simultaneously.
For example, turning to FIG. 1, a circuit 100, a prior art digital to analog (DAC) headphone playback channel, is illustrated. In the circuit 100, a pulse code modulation (PCM) codec 110 is coupled to a digital signal processor (DSP) 120. The DSP 130 is then oversampled at a demodulator (DMOD) 130, an output of which is coupled to an input of a digital to analog converter (ADC) 140. An analog signal of the DAC 140 is then conveyed to the driver 150, which is powered by a class “G” charge pump 160. This in turn, is used to power a pair of headphones 170.
However, as recognized by the Present Inventors, there are problems with this prior art circuit 100. Generally, the prior art circuit 100, as well as other circuits used for portable IC for an audio playback for a headphone (HP), encounter a problem of noise, be it white noise or other, within the DMOD 120, the DAC 140, and the HP 170, that forces tradeoffs between power dissipation, die size, and so on, versus a dynamic range of the circuit 100.
Certain patents do generally address power savings in a prior art circuit 100, used for portable IC for an audio playback for a headphone (HP). For example, please see U.S. Pat. No. 7,808,324 “Operating environment and process position selected charge-pump operating mode in an audio power amplifier integrated circuit” to Woodford et al, which is generally directed towards Class G efficiency, but not SNR or power of DAC, HP amp. U.S. patent application Ser. No. 11/610,496 “Energy-Efficient Consumer Device Audio Power Output Stage” to Tucker et al, is generated directed to a low power audio playback path focused on CP mode control, but no description of dynamic range improvement or power reduction occurring simultaneously. U.S. Pat. No. 7,622, 984, “Charge pump circuit and methods of operation thereof” to Lesso, et al, describes charge pump circuits to generate a plurality of positive and negative outputs using a single CFLY, but simultaneous DR improvement and power reduction is not addressed. U.S. Pat. No. 7,714,660, entitled “Amplifier circuit and methods of operation thereof” to Lesso et al, which is generally directed to a charge pump and headphone amplifier circuit which is directed toward improving “efficiency”, but does not address dynamic range, instead 660 is used to control CP mode of operation to track the signal amplitude. Other references are U.S. App. No. 2011/0123048 “Class G Audio Amplifiers and Associated Methods of Operation” to Wang et al, and U.S. Pat App No. 2011.0084760 A1 to Guo, et al, may be directed to class G amplifiers, but they do not address a dynamic range improvement or power reduction occurring simultaneously.
Therefore, there is a need in the art to address at least some of the issues associated with dynamic range improvement or power reduction occurring simultaneously.